Lecture 17 - Thrombosis I Flashcards
Thrombosis =
the formation of a solid mass from the constituents of the blood within the living circulation
Haemostasis =
the mechanism that leads to cessation of bleeding from a blood vessel
Pro-haemostatic factors:
Primary: vasoconstriction, thrombogenic subendothelial ECM
Secondary: coagulation cascade to produce fibrin, permanent plug
Antithrombotic factors
release of t-PA (fibrinolysis), thrombomodulin to block coagulation cascade
How does thrombosis occur in arterial circulation?
Associated with atherosclerosis.
Thrombus: small, pale, composed of platelet and fibrin in arteries with fast flow; tiny, made of platelet in capillaries
How does thrombosis occur in venous circulation?
Large, red, fibrin rich thrombus in low-pressure venous system
What are the visual characteristics of a thrombus?
Lines of Zahn (cell poor and cell rich layers)
Which conditions predispose to thrombosis according to Virchow’s Triad?
Changes in vessel wall, changes in local blood flow, change in coagulative qualities of the blood
Why does change in the vessel wall predispose to thrombosis?
Loss of endothelial integrity -> expression of pro-thrombotic factors
What is released by endothelium to stop thrombosis?
Heparin (enhances activity of antithrombin), TPA (activates plasminogen), prostacyclin (dilates vessel and disaggregates platelets)
What can lead to increased platelet numbers?
Major injury, surgery, post partum
What are platelets?
Circulating nuclear fragments of the cytoplasm derived from megakaryocytes
Which two sorts of cytoplasmic granules do platelets contain?
Alpha granules and dense bodies
To what to platelets adhere?
collagen exposed by endothelial damage
How to platelets release?
by degranulation of the platelets
